The invention relates to a method of providing the surface of base bodies of displacement or angle measuring systems with magnetizable material.
Until now, the respective magnetic tracks for displacement or angle measuring systems with magnetic graduation were realized by placing magnetizable rings on a base body, which could have consisted of steel for example. However, it is problematical in this case that, at very high rotational speeds, there is the risk of the rings becoming detached from the base body. In the technical field of protective coatings, there is also a known method of thermal spraying in which protective coatings are applied to base bodies by material particles, usually in the form of powder, being applied to substrates under a thermal influencing effect. Furthermore, it is also known from U.S. Pat. No. 5,391,403 to apply magnetizable material in this way to sensors for displacement measuring systems.
It is an object of the present invention to develop a method of the type identified at the outset of this application in such a way that the base bodies of measuring systems provided with magnetizable material are immune to detachment of the magnetizable material even under strong influencing effects, such as occur in particular at very high rotational speeds for angle measuring systems. This object is achieved by using a magnetizably material coating comprising a mixture of ferrite or materials comprising rare earths and a metallic component, whereby the composition of the magnetizable material is changed continuously from the beginning to the end of the spray application in such a way that the proportion of ferrite or of the materials comprising rare earths is chosen to increase from the beginning to the end of the spray application.
In a preferred embodiment of the invention the coating is applied in conjunction with a uniform rotating motion of the base body. As a result, a uniform coating with the magnetizable material is achieved and further the depth of the layer thickness can be achieved with precision.
A further preferred embodiment of the invention contemplates the magnetizable material being sprayed on in the form of a powder in a grain size of 1-100 xcexcm. It has been found that in this case an extremely good bonding of the sprayed-on magnetizable material with the surface of the base body, and also of the magnetizable material with itself, is made possible. If the spraying of the magnetizable coating material occurs under a vacuum, this effect is further enhanced, since no impurities from the atmosphere impair the bonding between the magnetizable material and the base body.
An additionally very advantageous feature of the invention involves roughening the surface of the base body before the coating is applied. This increases still further the adhesive strength of the magnetizable material on the base body.
Yet another advantageous feature of the invention is that after applying the coating to a base body, the coated base body is subjected to a heat treatment. This causes the magnetizable material to be transformed from an amorphous structure to a crystalline structure. Such a recrystallization annealing improves the preconditions for later magnetization which may be enhanced if need be by simultaneously applying an external magnetic field.
The surface of the base body coated with the magnetizable material is advantageously brought to a desired size by grinding, since this avoids damaging the applied surface layer, as can occur with other working methods, for example turning.
A further advantageous feature of the invention is that a number of magnetic tracks, required according to a particular use can be impressed into the coated base body. In this way the number of desired magnetic tracks does not have to be fixed until directly before use of the coated base body.
A particularly advantageous technical use for the invention is for the base body to be in the form of a coated steel hub for use as a measuring wheel in a magnetoresistive rotary transducer system.